1. Field of the Invention
The present invention relates to a nonrestoring divider. More particularly, it relates to a high speed circuit construction by which a circuit for predicting a partial quotient is formed by a lesser amount of hardware.
2. Description of the Related Art
Conventionally, a nonrestoring divider system is used as one element of a divider system. In a nonrestoring divider, sets of quotients used for forming digits of the quotient are previously determined and each digit of the quotient is selected from sets of quotients that do not include a zero, whenever possible.
These particular sets of the quotients excluding zero are usually expressed as follows, wherein "r" represents the radix. EQU -(r-1), =(r-2), . . . , -1, +1, . . . , r-2, r-1
In many calculators, calculation is carried out by using an operation unit having a plurality of bits rather than just a one-bit operation unit, and obviously, a radix larger than 2 is used. For example, the radix is 4 in a 2 bit unit, and 8 in a 3 bit unit.
Generally, an operation unit of l bits can be expressed as having an m digit number r as the radix, and is determined as: EQU r=2.sup.l/m
A characteristic feature of nonrestoring type division is the use of a negative number as well as a positive number in the partial remainder which results from a previous operation in which a digit of the quotient is determined. Also, the dividend (or partial remainder) or multiple of the dividend (or partial remainder) is added or subtracted by the sign of the dividend (or partial remainder) by using the negative or positive number in the result of the operation.
For example, the values which result from multiplying the division by k [where k=-(r-1), -(r-2), . . . , -1, +1, . . . , r-2, r-1] are set in registers, these registers are selected by a predicting signal output from a partial quotient predictor, and the quotient is obtained by repeatedly adding or subtracting the value which results from multiplying the division by k.
In such a nonrestoring divider system, when the number of bits "n" used as the operation unit becomes large, the radix is increased, for example, to 2n, so that the number of operation repetitions can be decreased and high speed operation can be expected. However, the multiplying of the divisor becomes complex, and therefore, the predicting logic for the quotient must be precise, which brings about a problem in that the number of circuits must be considerably increased. Furthermore, with respect to the logic for predicting the partial quotient, a method has not been developed in the prior art for forming an effective predicting circuit for the partial quotient.